It is known that reproducing images on a photosensitive medium, printing on a negative photographic paper for instance, in its most traditional aspect, consists of placing said paper in a light-proof room and then exposing it with light, carrying information concerning the image to be printed.
Said light can be generated by a lamp of a suitable power and colour temperature, and is conveyed by an optical device through a film carrying a negative reproduction of the image to be printed, and then to the photosensitive surface of the photographic paper.
The printed image is now in a latency condition and it must be subsequently developed and chemically fixed.
According to further reproduction modes, equally known to a medium-skilled technician, the photosensitive medium can consist of auto-positive photographic paper, either self-developing or not. It can be exposed with a light beam that lightens a film carrying the positive image, and then the photographic paper for a period of a predefined length, or by a direct exposure of the subject to be photographed, by means of a suitable photographic camera.
A common problem of the above mentioned techniques is that it is not possible to have a preview of the reproduction results. That means, it is not possible to see whether the reproduced image quality will be satisfactory, before the photosensitive paper has been developed.
This can be in many cases a non-easily solvable problem. For instance, in those photo studios where a document-format, snapshot pictures service is provided, the result quality depends on several factors. Some of these are easily controllable, like the apparatuses and materials quality, or the subject illumination; some other factors are more casual, like the subject expression during the camera click, or a subject eyes blink just at that moment. A bad issue of the picture will surely disappoint the client, or it will force the photographer to repeat the whole process. This will obviously cause a wasting of time and of photographic material.